The present embodiments relate to a local coil for a magnetic resonance system and a method for indicating a change in the state of the local coil.
Local coils are used increasingly frequently in modern magnetic resonance facilities. Signal quality may be improved when the coil conductors receiving the magnetic resonance signals are positioned closer to the object to be recorded. Such local coils are known as transmit coils, receive coils, and also combined transmit and receive coils.
To read or activate local coils, it is usual, in order to avoid long cable runs, to connect the local coils by a connector apparatus, such as a plug, to a plug-in station on a patient couch of the magnetic resonance facility. A patient couch may have, for example, eight plug-in stations, which are disposed according to frequently used positions for local coils.
For correct activation, energization and/or data evaluation, the system knows which type of local coil (for example head coil, body coil, back coil, etc.) has been connected to a plug-in station. Two methods are used for providing information about the connected local coils.
First, it is possible to identify a local coil connected to a magnetic resonance facility using an analog method. Here resistors are used, the resistance value of which can be read out so that the magnetic resonance facility identifies the coil type with the aid of corresponding software. Two resistors may be used for example. From the two resistance values, it is possible after analog-to-digital conversion to generate a 1-byte code. The 1-byte code may be used to identify the coil type. However coil-specific data, such as serial number, product status, manufacturer and the like, are not disclosed with such systems.
When using such analog coil code resistors, it is possible also to inform the magnetic resonance facility of a state change of the local coil. This can be done by embodying the resistance values in a switchable manner so that a change in the resistance value therefore also results in a change in the 1-byte code. The code is used by the magnetic resonance facility as a pointer to a certain file (information). The file describes how the code should be interpreted (“which coil is connected?”). This change in the resistance value informs the magnetic resonance facility of a state change of the coil and the content of the change. Possible state changes are for example (excessive) temperature of critical components, orientation of the local coil, switch positions at the local coil, and/or the combining of the local coil with other parts (e.g. head coil upper part and head coil lower part).
However, this procedure with analog resistors also has disadvantages. The connection of the local coil to the plug-in station and also a change in the detected resistance values are identified by a discriminator circuit. Such a discriminator circuit is susceptible to the unwanted injection of gradient or high-frequency signals, as occur regularly in a magnetic resonance facility. This can lead to an incorrect response on the part of the magnetic resonance facility, for example deactivation during a sequence. A change in the resistance values during the sequence run-through results in the sequence being terminated.
Also when resistance values are used, it is not possible to implement a specific trigger signal or interrupt signal, upon which the local coil informs the magnetic resonance facility about a state change. For, ultimately, detection of the resistance change represents an association with interrupt generation (state change, in other words termination of the sequence) and information about the type of state change, both being implemented in a single function. This is disadvantageous, because additional resistance codes are used and these are not available in very large quantities with analog resistors. Every change of state is necessarily always associated with the generation of an interrupt signal or trigger signal. This makes the interface inflexible, as only state changes that are to be allowed to result in a sequence termination can be mapped.
Finally, as mentioned above, it is not possible via the implementation of an analog interface with resistance values to provide coil-specific data. Such data is useful for example in asset management or when tracking individual local coils and when specifically matching a magnetic resonance facility to specific local coils. An implementation with analog resistors would be conceivable but very complex and extremely ineffective.
The second known variant for identifying a local coil connected to a magnetic resonance facility is a digital interface, with which a digital storage module, for example an EEPROM (Electrically Erasable Programmable Read Only Memory), is used. Further information in addition to the information about the coil type (coil code) can be stored in such storage facilities. The disadvantage of such an implementation is that once the data is stored on the storage facility, the information is fixed. The information can no longer be changed. The use of storage facilities, the content of which may be changed by the local coil itself, would be expensive and ineffective. When using a digital interface, (e.g., a readable storage facility), state changes of the coil may not be disclosed to the system.